The common practice in the field of portable navigation is the use of GPS-only systems. The position and/or velocity information from the GPS receiver is displayed on a digital map to identify the location of the user. However, GPS is not reliable as it needs a direct line of sight to at least four different GPS satellites and the line of sight may be interfered with, for example by trees when in a forest or blocked, for example when in a tunnel.
Inertial sensors are self-contained sensors that sense the changes in accelerations and angular rates of the conveying body. These sensors are sometimes used to bridge the GPS signal outages if they are tethered with the moving body in a well defined orientation. The tethered and well aligned constraints make the device application specific and not user friendly.
Navigation when using an assembly of inertial sensors has heretofore involved the use of different navigation algorithms for different transit/conveyance modes. Consequently, there has been no commercially available system known to us that can provide seamless navigation (position, velocity and attitude) information, when multiple modes of conveyance are involved, due to the fact that different algorithms have been used. More specifically, the on-foot mode of transit is implemented by using pedestrian dead reckoning (PDR) algorithm to avoid the huge drifts associated with the integration of inertial signals. However, PDR requires assumptions that must be satisfied for all type of walking modes. For example, climbing up the stairs require different assumptions for stride length and step detection threshold than going down the stairs. In addition, the in-vehicle navigation mode cannot be implemented using PDR and needs mechanization algorithm. Hence, two algorithms are used for the two most common transit modes. It is important for the system to recognize the appropriate mode of transit to switch between the modes otherwise the system will not work well. A mechanization algorithm for on-foot is not desirable due to the quadratic drift of derived navigation parameters with time. This problem has been resolved in the prior art as follows:                1) Use of wireless only positioning (GPS or cellular signals triangulation) for different transit modes (such as positioning used in iPhone). Wireless positioning has only one algorithm no matter what the mode of transit is. However, as previously stated, wireless signals require line of sight to four different signal sources (such as four GPS satellites in case of GPS positioning) to provide a position. Unfortunately, this condition cannot be satisfied all the time;        2) Use of a physical switch, such as cables or tethering inside a land vehicle, to ensure that mechanization algorithm is used for in-vehicle navigation. If in doubt, such systems use wireless only navigation. If wireless only navigation is unavailable, then the user simply doesn't get the navigation information; or        3) Design separate systems, if seamless positioning using inertial sensors is desired, for on-foot and in-vehicle navigation, to ensure the desired use of the navigation system.        